A touch pad is a data input device including a plurality of sensing points arranged in a matrix shape on a plane and capable of detecting a point touched by a user and a direction in which the touched point moves, and is thus widely used in place of a mouse. There are various types of touch pads including touch pads in which electrical switches are arranged in a plane, and touch pads in which capacitive sensors, resistive sensors, surface acoustic wave sensors, or optical sensors are arranged in a plane.
Among them, a touch panel comprising a plurality of touch pads using the capacitive sensors is widely used to control the movement of a cursor on a notebook computer. The surface of the touch panel is covered by an insulating layer, and horizontal lines and vertical lines are arranged at regular intervals below the insulating layer. The horizontal line and the vertical line are used to measure capacitance as an electrical equivalent circuit, in which the horizontal line is a first electrode and the vertical line is a second electrode.
When a conductive object such as a finger is in contact with a sensing surface, an electrostatic capacitance existing in the horizontal line and the vertical line has a different value from that in the other lines that are not in contact with the conductive object. For example, a voltage signal is applied to the horizontal line, and the voltage induced on the vertical line is measured to detect a change in electrostatic capacitance of the capacitor, thus determining which portion of the sensing surface is in contact with the conductor.
Another type of touch panel, a resistive 2D matrix touch panel, has a structure in which an electrical conductor is disposed in two-layer films and a minute space is formed between the two layers such that the two layers are not short-circuited. When a user touches a specific area with his or her finger, the conductors of the two layers located in the corresponding touch area are short-circuited with each other, and thus the touch panel detects a potential or current in the short-circuited area, thus determining the coordinates of the corresponding conductors.
At this time, a binary signal interpreted as either on or off is generated to indicate whether the conductors are short-circuited, and a plurality of binary signals are distributed around the touch area as large as the finger to allow the touch panel to determine the coordinates of the specific touch area.
Such touch panels are widely used in portable communication devices such as mobile phones, personal digital assistants (PDAs), portable media players (PMPs), etc. and electric household appliances such as kitchen appliances and humidifiers as well as notebook computers, navigation systems for vehicles, etc.
However, in the case where the finger is used to touch the touch panel, water present on the finger may drip onto the touch panel, and if the area thus contacted is large, a plurality of touch pads may be contacted. Here, the touch sensor device cannot determine an accurate touch position of the touch object.
FIG. 1 is a cross-sectional view of a portion of a conventional touch sensor device that may malfunction, in which a conductive material 5, a touch panel 10, a plurality of touch mark-keys B11 and B12 to BN1 and BN2, a plurality of touch pads 1P-11 and 1P-12 to 1P-N1 and 1P-N2, and a touch sensor 20 are provided. The plurality of touch mark-keys B11 and B12 to BN1 and BN2 are mounted on the top of the touch panel 10, and the plurality of touch pads 1P-11 and 1P-12 to 1P-N1 and 1P-N2 are mounted on the bottom of the touch panel 10.
The malfunction of the conventional touch sensor device will be described below with reference to FIG. 1.
For example, it is assumed that a user intends to select a desired function by touching a specific touch key B11 among the plurality of touch mark-keys B11 and B12 to BN1 and BN2 on the touch panel 10 of an electric rice cooker with his or her wet finger.
However, since the water on the finger is the conductive material 5, touch signal is also applied to an adjacent touch key B12 in addition to the specific touch key B11, and thus the touch sensor device determines that a touch object is in contact with both touch pads 1P-11 and 1P-12.
Therefore, the touch panel 10 receives touch information of the finger as the touch object from the two touch pads 1P-11 and 1P-12 and generates electrical signals sig2-11 and sig2-13 corresponding thereto, and the touch sensor 20 receiving the electrical signals sig2-11 and sig2-13 through the two touch pads 1P-11 and 1P-12 detects the positions of the two touch pads 1P-11 and 1P-12 and outputs the changes in electrical state as sensing signals s_sig11 and s_sig13, thereby causing malfunction.
Moreover, as another malfunction of the conventional touch sensor device, the touch object may touch the plurality of touch pads 1P-11 and 1P-12 to 1P-N1 and 1P-N2 only briefly but still exceed a predetermined time. For example, the user may sequentially touch the plurality of touch mark-keys B11 and B12 to BN1 and BN2 while brushing a duster across the touch mark-keys to remove foreign substances from the touch mark-keys on an electric household appliance.
However, although the user intends only to remove the foreign substances from a specific touch key, touch signal is also applied from the user's body to adjacent touch mark-keys, and thus the touch sensor device determines that the touch object is in contact with the corresponding touch mark-keys contrary to the user's intention.
Thus, the touch panel 10 receives touch information of the touch object from the touch pads connected to the specific touch key and the adjacent touch mark-keys and generates electrical signals corresponding thereto. Then, the touch sensor 20 receives the electrical signals through the corresponding touch pads, detects the positions of the corresponding touch pads, and outputs the changes in electrical state as electrical signals. As a result, the functions corresponding to the touch mark-keys are performed regardless of the user's intentions, thus causing malfunction.